The modern orthodontic bracket was developed by Dr. Edward Hartley Angle and became commercially available in the early 1900's. In spite of significant improvements in design, materials and manufacturing processes that have occurred since Dr. Angle's time, the biomechanical functioning of orthodontic brackets remains essentially unchanged.
A variety of orthodontic brackets have been designed over the years generally incorporating varied bonding bases connected to an orthodontic bracket body. The bonding base is connected to the bracket body by brazing or other means or a bracket can be fabricated as an amorphous one-piece unit. The bonding pad provides the interface for a mechanical bond between the bracket and the tooth. Once the brackets are bonded to the teeth, orthodontic wires are installed in the bracket's arch slots.
Normally a bracket or set of brackets are bonded to teeth and orthodontic wire(s) are engaged which will move teeth to predetermined positions according to a treatment plan created by an orthodontist. In order to engage the archwire in the arch slots of a series of brackets, it is common to use elastomeric, steel ligatures or other means of ligation to retain a sequential series of archwires typically needed during the course of orthodontic treatment. Conventional ligatures are looped or lassoed over the tie-wing structures of each bracket thus positively retaining the archwire in its corresponding slot in the bracket(s).
Central to the tooth-moving function of the orthodontic bracket is the archwire slot. The archwire slot is a horizontally oriented, outwardly opening trough spanning a bracket's labial or buccal face. Archslots should be understood as having a floor and two parallel walls perpendicular thereto, where the floor and walls define a rectangular configuration in cross section. Such a rectangular slot is intended to accept a correspondingly sized rectangular archwire. Orthodontic archwires, fabricated from resilient metallic materials generally are sized to matingly fill a bracket's archslot. In doing so, the archwire further provides continuity to the overall arch shape as it extends around the dental arch.
The rectangular and inter-fitting relationship between an archslot and its archwire is the defining characteristic of a system of orthodontic armamentarium used for a treatment methodology known as Edgewise Orthodontic Therapy. The Edgewise technique was developed by Dr. Angle and his contribution is substantial. Others, Including Dr. Lawrence F. Andrews have advanced the Edgewise bracket to its current high level of bioengineering
To describe the biomechanical functioning of modern orthodontic brackets, the following description is provided: First, it must be understood that the orientation of the archslot as it transverses the face of a bracket is established for each type of bracket during the manufacturing process. Statistically determined values for torque, angulation, prominence and intrusion/extrusion are incorporated into the positioning of the archslot on a tooth-by-tooth basis. Second, reference for such statistical archwire positioning data is keyed off of both the archwire (as a datum) and off of anatomical guideposts on the teeth themselves. Ideally, such studied bioengineering of the archwire/bracket/archslot relationship leads to perfect alignment of the teeth and a perfectly straight and “spent” archwire at the end of treatment. As above, Dr. Lawrence Andrews advanced Edgewise Therapy in the 1970's. In orthodontics his treatment methodology is in fact well known as “Straight Wire” because of the functioning of such a system of rectangular slots and wires, ends in a straightened archwire at the conclusion of treatment.
The archwire and bracket system have an inter-working physiologic relationship. At the end of orthodontic treatment each tooth can be visualized as being in ideal relation to its adjacent teeth and its opposing teeth, with all the teeth aligned and in ideal positions according to an ideal archform. In such an ideal configuration, all of the walls of each bracket's archslot can be considered as being coplanar, defining a plane approximately parallel to the occlusal plane. Further, the center point of the floor of each archslot can be thought of as being tangent to an elegantly shaped natural archform. It is instructive to next consider such an orderly system of archslots as time is reversed, and the case is slowly returned to its pre-treatment condition. As this happens, the teeth all slide back to their original chaotic mal-positioned pre-treatment orientations taking the brackets attached to them with them. The archslots fall out of relation to each other and become as mal-positioned as the teeth they are attached to. The above exercise conceptually illustrates both the final objective and the starting condition of treatment in terms of archslot orientation.
It is the orthodontist maneuvering the archwire into the series of archslots at the beginning of treatment that provides the motive force for correction. As the archwire is forced into the arch slots via twisting and bending, energy is stored in the archwire as it is deflected this way and that. It is the slow dissipation of that stored energy that provides the continuous, gentle forces that desirably move the teeth into desired positions.
Not all archwires used in Edgewise Therapy are rectangular in cross-section. Edgewise orthodontic treatment calls for the use of a progressive series of archwires. Typically, smaller, round wires are used at the beginning of treatment. Such wires exhibit a low spring rate and low modulus, and are capable of handling the large bracket-to-bracket deflections encountered at the beginning of treatment without taking a set. Round archwires used early in treatment are not considered as being true Edgewise wires because being round in cross-section, they are incapable of imparting tortional correction forces against the flat slot walls and floor. In orthodontics, this type of force acting on the roots of the teeth is called “torque.” To clarify this point, it must be understood that had such wires been used at the beginning of treatment, significant patient discomfort would have resulted, along with insult to the periodontal membrane surrounding the root of the tooth. Such round wires are nonetheless very capable of rapidly moving the significantly mal-aligned teeth in terms of intrusion and axial extrusion, rotation and tipping to begin the process of unscrambling the occlusion. The phase of treatment where the attending orthodontist may use a series of relatively small, but progressively larger and stiffer round wires is known as “first phase orthodontics” or the “leveling phase.”
Later in the treatment sequence, after multiple round wires have been employed, an orthodontist may utilize the first of a series of true Edgewise wires. These archwires typically exhibit a higher spring rate and are therefore significantly stiffer. Such wires are incapable of spanning the large deflections encountered earlier in treatment without exceeding the effective physiological force range for tooth movement. To clarify this point, it must be understood that had such wires been used at the beginning of treatment, significant patient discomfort would have resulted, along with insult to the periodontal membrane surrounding the roots of the teeth anchored in the alveolar supporting bone. Further, such an archwire used inappropriately early in treatment would be likely to take a set and matallurgically yielding.
As can be appreciated, the use of larger, harder, square and rectangular archwires can only be initiated after significant orthodontic correction has been achieved. Importantly, since such wires do exhibit a square or rectangular cross-section, they are capable of beginning the positioning of the teeth in terms of torque. Torque is the motive force that swings of the root structure of the tooth though the supportive bone while holding the crown portion stationary. As described above, round wires are not capable of imparting torqueing forces to a tooth because they lack features needed to engage the Edgewise configuration of the archslot and therefore, they can only tip teeth around an unseen center of resistance in the supporting bone.
An orthodontist may begin the true Edgewise phase of treatment with an archwire with dimensions of 0.016×0.016 inch. As the 0.016 inch square archwire achieves a degree of response over a period of a few weeks, it will in turn be replaced by an archwire of slightly more robust dimensions such as of 0.017×0.021 inch. Again, Edgewise wires have mechanical properties that are distinctly different from the wires used at the beginning of treatment. The full-sized Edgewise finishing wires used during the final stages of treatment can be formed from highly work-hardened stainless steel and may exhibit a modulus of stiffness exceeding 3×107 and have a tensile strength approaching 300 KSI UTS.
As can be appreciated from the foregoing, and as related to the present invention, a significant portion of the entire time allotted for an individual patient's treatment is devoted to the routine steps of installing and removing a progressive series of archwires. Historically, changing an archwire and replacing it with the subsequent archwire has involved first cutting and removing typically twenty steel ligatures. Ligature wires are formed from dead soft stainless steel and are commercially available in diameters ranging from 0.009 to 0.012 inch. In addition to cutting and removing each tiny ligature wire from each bracket, a new ligature wire must be tied onto each of the typically twenty brackets. The tying step required by steel ligatures involves first lassoing the bracket, then tightly twisting, and then cutting off the excess. The remaining twisted section must be tucked under the tie-wings of the bracket to avoid laceration of the soft tissues of the tongue, cheeks and gums.
Orthodontic bracket bodies have been designed in a variety of geometries or shapes. The most common bracket used in orthodontic treatment has been a twin or Siamese-design, where there are at least two sets of tie wings located at each end of the archslot. These are referred to as the mesial tie wings and the distal tie wings. Ligatures typically pass from the occlusal tie-wings, up and over the archwire/archslot, extending to the gingival tie-wings where they are twisted, cut and tucked under the occlusal tie wings. In this manner ligatures hold the archwire down into the archwire slot. The tie-wings also support other structures such as hooks for elastics and the tie-wings themselves can serve as a sort of macro hook, accepting the loops of elastic chains and the like.
Additionally, other ligature systems fixate orthodontic wire into a bracket archwire slot to enhance orthodontic treatment. These ligature systems often require an alteration or variation of the bracket body design, pad design, slot dimensions or other bracket geometries traditional with a twin tie-wing bracket which have been commonly accepted and proven to work in providing optimal force delivery to complete orthodontic treatment.
Since such a large portion of an orthodontic patient's time in the orthodontist's chair is consumed by changing archwires in this manner, and since such routine archwire changes constitute a major cost to the orthodontic practice and contribute to the cost of treatment for the patient, much inventive effort has gone into identifying innovative chairside systems that reduce the time and cost associated with archwire changing.
One innovation introduced in the mid-1970's was the commercial introduction of elastomeric ligatures. Injection molded from elastomeric polymers such as urethane, elastomeric ligatures form a tiny toroidal “o”-ring shape, and exhibit elastic properties so they can be stretched over the ligation features of an orthodontic bracket. Use of such elastomeric rings introduced some timesavings by eliminating the steps of cutting, tying and tucking of the traditional steel ligatures. Further, the elastomeric ligatures are available in a rainbow of colors as well as clear, black and glow-in-the-dark. Such an array reportedly adds a means for patient self-expression and an element of fun for orthodontic patients.
The use of elastomeric O-rings however introduce new difficulties and concerns. For example, they can discolor and stain and they can lose their tractive force capabilities as they absorb water in the mouth. In general, their biocompatibility, particularly as related to certain plasticizers they may contain to enhance their latex rubber-like properties has been brought into question in the orthodontic literature. Further, like the steel ligatures, the elastomeric ligatures require special dedicated instruments for placement, even though some orthodontists use standard instruments. In either case, any instruments for ligature placement must be sterilized after each use, thus requiring specific in-practice procedures which involve measurable cost.
The present invention is related to yet another path of innovation directed toward mitigating the time-consuming problems and cost associated with routine changing of archwires. Orthodontists have long sought out a bracket design that incorporates features where no ligature whatsoever is required to capture and retain the archwire in the archslot. This has led to the advent of the self-ligating orthodontic bracket. The present invention introduces desirable improvements over conventional self-ligating brackets as described below.
Prior art disclosing some form of self-ligating orthodontic brackets is found in U.S. Pat. Nos. 2,011,575; 3,772,787; 4,248,588; 4,492,573; 5,474,445; 6,071,118; 6,368,105; and 6,168,429.
In reviewing the general field of self-ligating brackets, both proposed and commercialized, it can be said that all versions that employ a vertically-sliding clip inherently compromise patient comfort. Patient comfort is compromised through the use of such brackets due to the fact that overall bracket prominence must be increased in order to accommodate the increased labial-lingual or buccal-lingual thickness of the bracket driven by the addition of a vertical slot. Being centrally located, such vertical slots incorporated into the bracket body are typically positioned adjacent to the labial-most or buccal-most point on the clinical crown of a tooth, and are therefore directly additive to the final position of the soft-tissue-contacting surfaces of such an orthodontic bracket.
Generally, commercial offerings of conventional Straight Wire Edgewise bracket systems are available grouped according to a bracket prescription. Such a bracket system or bracket prescription represents a discrete series of values for each bracket in the system. For example, a particular prescription may callout that for a maxillary cuspid bracket, its archslot shall be oriented according to a torque value of −2° and oriented to an angulation value of 13°. The same prescription may specify that the center of that bracket's slot floor is outset 0.023 inch from the enamel surface of the crown. The lateral tooth in the same prescription may call for an archslot that is oriented at 8° of torque, 9° of angulation, but outset from the lateral crown by 0.044 inch. Of importance for differentiation of the present invention, the reader should note the significant difference in the outsetting of the archslot, where in this example the cuspid archslot is outset only 0.022 inch whereas the lateral bracket's archslot is outset over half a millimeter further out from the tooth enamel.
A complete prescription will include torque, angulation and outset values for all of the set of twenty brackets. Such bracket system prescriptions are based on statistically determined norm values obtained from the human population, but many variant prescriptions have emerged influenced by research and the various investigators' assessment of stability, aesthetics, treatment protocol and so forth. Today, perhaps eighteen distinct prescriptions are commercially available to orthodontists. Accordingly, orthodontic manufacturers offer various types of bracket designs, each in multiple prescriptions.
As above, all prescriptions for orthodontic bracket systems include discrete values for the out-setting of the arch slot according to prominence values. Of all such values incorporated into such prescriptions, prominence is accepted as the most relevant value impacting patient comfort as well as the design continuity of the entire bracket system. To amplify this point, during orthodontic treatment brackets are bonded to the teeth and in position, they extend outward against the inside of the cheeks and lips. Subtle aspects involving the effective smoothness and particularly the prominence of the brackets greatly impact patient comfort/discomfort. The degree to which the presence of brackets irritates the opposing soft tissues has been demonstrated to directly correlate with bracket prominence. Pressure sores, erosion of tissue and even severe lacerations have been reported. In some cases these problems become so severe that orthodontic treatment must be curtailed all together. Because of the central concern that patients must be able to tolerate the orthodontic hardware in their mouths, commercially available bracket systems are bio-engineered with a very high emphasis placed on making the bracket system as low in prominence as the structural limitations of the materials and processes used to manufacture the brackets will permit.
As described above popular bracket systems inherently include certain brackets that are the shortest in stature (typically the cuspids or sometimes the mandibular second bicuspids) and conversely, they will contain the tallest brackets (typically the upper laterals). An engineer's task in designing such a bracket system is to focus on the most structurally challenged brackets of the system, which in turn are the lowest prominence (shortest) brackets. It is ultimately the structural considerations implicit within the design of these lowest brackets of the series that then predicts the height of the entire series. An explanation of this relationship follows.
As a bracket system is engineered, it is the structural considerations relating to the minimal thickness of (steel) material under the archslot required to avoid structural failures such as wing bending or archslot spreading or inward collapse during treatment that must be considered. Children at orthodontic treatment age (ten to fifteen years) live very active lives and are involved in sports and all sorts of rough activity. As orthodontic patients, they unfortunately pay little attention to instructions from their attending orthodontist to avoid putting certain types of things in the mouth (popcorn, frozen candy bars, crunching ice, etc.). The structural demands placed on orthodontic brackets and orthodontic armamentarium can be severe. Metallurgical strength and structural stiffness needed to withstand such destructive forces are measured in terms of the unit strength of the material along with its modulus, tensile and compressive strength properties.
Advanced biomedical alloys are used in the fabrication of orthodontic armamentarium, including work hardened stainless steel, titanium, chromium-cobalt alloys and the heat-hardenable alloys of stainless steel such as 17-4 and 17-7 PH. Overall, orthodontic brackets are highly engineered to be as low in prominence as such specialty metals will permit. Distortion of brackets during treatment resulting from trauma mastication, bruxism, mechanical interference between teeth and other brackets, and distortion caused by such things as “sports accidents” all must be anticipated from a structural design standpoint. Again, the “Achilles heel” of orthodontic brackets is the thin structure under the archslot. It is on this area that destructive forces are concentrated and it is at this point that a bracket may structurally yield to those forces. To appreciate the advantages of the present invention, it must also be understood that the amount of structure under the archslot also directly predicts the overall height of a bracket. The reader can then appreciate that overall bracket design is driven by some very demanding design criterion that are directly at odds with each other. If brackets could be designed with higher prominence, they could much more easily withstand destructive forces but their higher prominence would result in unacceptable levels of patient discomfort.
So, any bracket system's design is driven by those particular brackets within its prescription that are most vulnerable to distortion and structural failure. Stated differently, it is the lowest bracket in the system that defines the “structural minimum” of the system, and in doing so, it thereby defines the height of all of the rest of the brackets. Stated differently again, after the structural requirements have been established for the structural minimum of a system of brackets, the prominence values for the rest of the brackets of greater prominence can be established according to the exact outset values of the bracket's prescription. It can be said that for all of these reasons then, it is paramount that orthodontic brackets be designed at the absolute minimum prominence consistent with structural survivability in the mouth.
Since prior art self-ligating bracket designs center the vertically siding clip directly over the labial-most or buccal-most point on the tooth crown, the thickness of the clip itself, and the labial-lingual dimension of its vertical channel contribute additively to what engineers call “material stack.” For example, the dimensions of a vertical slot, passing in a occlusal-gingival direction may be 0.012 inch in a labial-lingual dimension. Establishing the thickness of the bracket material between the ceiling of such a vertical slot and the floor of the main horizontal archslot involves considerations of stresses on brackets during treatment as described in detail above. This area of the bracket's structure represents the location of the Achilles heel where the destructive forces are concentrated. In the case of prior art self-ligating brackets with vertically sliding self-ligation features, the body of the bracket must be correspondingly outset from the tooth to accommodate these features between it and the tooth surface.
Unlike the present invention, in order for prior art brackets to gain the function of self-ligation, they become inherently higher in prominence by at least the labial-lingual dimension of the vertical slot through which their clip slides.
These prior art ligature systems are designed to fixate or hold an archwire into a bracket slot without requiring the use of separate elastomeric or wire ligatures to fixate or attach an archwire into a bracket slot. This allows the orthodontist to keep an archwire ligated or fixated into a bracket archwire slot without changing and applying separate elastic or steel ligatures. This allows for some time savings and clinical efficiencies during the course of orthodontic treatment. Such advances, however, can ultimately prove useless if self-ligation features drive the height of a bracket system to an unacceptable level where a patient cannot tolerate them.
Some of the enhanced mechanical advantages promulgated by the inventors of prior art self-ligating bracket designs include the fact that self-ligating features that engage only the bracket body and thereby do not come in contact with the archwire during treatment greatly reduce bracket friction. Such a lack of direct archwire contact is claimed to reduce or eliminate mechanical friction caused by the tendency of conventional ligatures tendency to forcefully pull an archwire hard against the arch slot floor. The orthodontic literature contains many reports reinforcing these claims that bracket to archwire binding slows tooth movement and adds to the overall length of a patient's treatment. The present inventive assembly likewise does not force the archwire against the archslot floor and in fact, an archwire contained within the present inventive bracket remains unrestricted in all axes other than the confines described by the rectangular volume of the archslot.
Even though many prior art self-ligating bracket features may desirably reduce friction and mechanical binding, they nonetheless require a deviation away from the useful twin or Siamese-type bracket design that incorporates two sets of tie-wings. Such prior art self-ligating designs are limited and incapable of delivering certain corrective forces to the teeth. Some of these alterations are designed to allow the archwire ligation mechanism space to be incorporated as part of the orthodontic bracket and work to ligate the archwire into the archwire slot. These alterations can compromise the benefits of utilizing a twin orthodontic bracket.
Some of the current self-ligation brackets have designs that are not easy to use during the course of orthodontic treatment. They can be harder to space to disengage the orthodontic wire during treatment or to allow for the next sequential archwire to be space-engaged in its place. Therefore special instruments may be needed to be used to open and sometimes close the ligation mechanisms to allow for archwires to be removed and replaced to progress the course of orthodontic treatment.
The self-ligation capability of some known self-ligating bracket systems works efficiently only later in treatment after the teeth have been sufficiently aligned. High angles of archwire deflection as an archwire enters and exits the archslot of such a bracket cannot be accommodated. Highly deflected archwires, such as those typically used early in treatment can circumvent such self-ligation features thereby causing special problems for the orthodontist and greatly compromising the otherwise positive advantages of self-ligation.
Some of the current self-ligation brackets require additional springs or inserts to be incorporated into the design in order to facilitate the ligation function. This allows for the ligation mechanism to stay open or closed reliably and predictably during the course of treatment.
Some of the current self-ligation brackets do not allow for the ligation cover to be removed during orthodontic treatment. Additionally, if the ligation cover comes off the bracket body for some reason during treatment, the ligation cover can not easily be put back in its place to continue the course of treatment without having to remove the entire bracket from the tooth and replace it with a new bracket.
Prior art bracket assemblies can also have clips that undesirably pop open or can be difficult to open or close.
One difficulty of prior art self-ligating brackets is that they tend to become encrusted with calculus, plaque and oral bacteria. A central vertical channel in prior art brackets tends to provide a particularly good harbor for bacteria because of little flushing by saliva and the propensity for plaque to become established and to harden. Such a configuration makes it impossible to get a toothbush in place to reach such small internal features. It is known that all too often, the clips of prior art self-ligating brackets become bound up and locked in place due to buildup of hard plaque deposits. Patients having these types of self-ligating brackets are often instructed to rinse frequently with an anti-plaque rinses to help reduce the frequency of jammed clips.
On the other hand, the two channels of the present invention, being on the external mesial and distal edges of the bracket are much more accessible, and are therefore irrigated with saliva much more readily. Being on the outside surfaces of the bracket, these features can be reached by a toothbrush or irrigated with a water pik. This aspect of the present invention greatly reduces the undesirable likelihood of the clip becoming locked in place due to plaque deposits. The brackets of the present invention provide a greatly reduced potential for compromised oral hygiene during treatment due to the lack of features that can provide and harbor oral bacteria.